Relative Mass And Mass Spectrometer

Question 1

Relative atomic mass (Ar) definition

Answer 1

Average mass of an atom of an element relative to carbon 12

Question 2

Relative isotopic mass definition

Answer 2

Mass of an atom of an isotope of an element relative to carbon 12

Question 3

Mass spectrometer uses

Answer 3

Can find
relative molecular mass
Relative atomic mass
Relative isotopic abundance

Question 4

Mass spectrometer stages

Answer 4

Ionisation
Acceleration
Ion drift
Detection

Question 5

Ionisation types:

Answer 5

Electro spray ionisation

Electron impact ionisation

Question 6

Electro spray ionisation

Answer 6

Sample is dissolved
Pushed through small nozzle at high pressure
Each particle gains H+ ion
Sample turned to gas

Question 7

Electron impact ionisation

Answer 7

Sample vaporised
Electron gun fires high energy electrons at it
Knocks off one electron so become +1 ions

Question 8

Acceleration

Answer 8

Positively charged ions accelerated by electric field

So all have same kinetic energy

———> lighter ions will move faster than heavier

Question 9

Ion drift

Answer 9

Ions enter region with no electric field

Drift through

Lighter ions will move faster than heavier ions

Question 10

Detection

Answer 10

Ions with lower mass to charge ratio travel at higher speeds in drift region

Reach detector in less time than those heavier

Detector detects charged particles

Mass spectrum is produced

Question 11

Mass spectrum graph

Answer 11

Mass\ charge on x axis

Percentage abundance on the y axis

Question 12

Relative atomic mass calculation from mass spectrum

Answer 12

1. Multiply mass/charge by percentage abundance
2. Add all these up
3. Divide by 100 when using percentages

Question 13

Mass spectrometry used to identify molecules

Answer 13

Can get mass spectrum for molecular sample

1. Molecular Ion former from mass spectrometer when one electron removed from molecule
2. Gives peak in spectrum with mass/charge ratio equal to relative molecular mass of molecule
3. Can identify unknown compound